In the course of this investigation we propose to determine the changing spatial and functional relationships of the enzymes during germ cell differentiation. We will perform a systematic study designed to localize adenylate cyclase and guanylate cyclase in mouse and human testes during the several stages of germ cell development, in Sertoli cells and in Leydig cells. This investigation will also provide some insight about the hormone sensitive nucleotide cyclases. Adenylate and guanylate cyclases will be localized in mouse and human testes employing the technique developed by Wagner and Bitensky (1974). Cyclases sensitive to hormones and neurotransmitters will be studied by the method of Reik et al. (1970). The same methods will be employed to demonstrate the adenylate and guanylate cyclases activity in abnormal mouse and human testes. At the end of this project we shall have better understanding about the role of cyclases in the mechanism of the control of cell cycle events.